Rubber composition and heavy duty pneumatic tire using the rubber composition

ABSTRACT

A rubber composition obtained by compounding (A) a rubber component comprising 15 to 55% by weight of (i) a modified styrene-butadiene copolymer rubber which is obtained by solution polymerization and has a tin atom introduced into its molecular chain, 45 to 85% by weight of (ii) at least one rubber selected from natural rubber and synthetic isoprene rubbers, and (B) a hydrazide compound.  
     The rubber composition exhibits improved abrasion resistance, heat resistance and low heat generating property and is advantageously used for tread rubber of heavy duty pneumatic tires.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a rubber composition and a heavyduty pneumatic tire comprising the rubber composition. Moreparticularly, the present invention relates to a rubber compositionadvantageously used for tread rubber of heavy duty pneumatic tires and aheavy duty pneumatic tire comprising the rubber composition in treadrubber.

[0003] 2. Description of the Related Arts

[0004] To improve abrasion resistance and the life of a heavy dutypneumatic tire used for trucks and buses, it is important that rigidityof the tread is enhanced, a decrease in the life due to damages byoutside causes is prevented and elevation of temperature of tread rubberdue to repeated deformation during driving is suppressed

[0005] Heretofore, to increase the life of a tire, an amount of, forexample, carbon black, a resin, a vulcanizing agent such as sulfur, oran auxiliary vulcanizing agent used in the rubber composition isincreased. When the amount of carbon black is increased, however, thelow heat generating property and heat resistance inevitably deterioratealthough abrasion resistance is improved. When the amount of either avulcanizing agent such as sulfur or an auxiliary vulcanizing agent isincreased, heat resistance decreases while the low heat generatingproperty and abrasion resistance are not affected. When the amount of aresin is increased, abrasion resistance and the low heat generatingproperty deteriorate although heat resistance is improved. It is alsoknown that, when natural rubber exhibiting an excellent maximumelongation at high temperatures is blended with SBR exhibiting a highhardness at small deformations, a problem arises with respect to the lowheat generating property although abrasion resistance and heatresistance are improved.

[0006] For tread rubber of heavy duty pneumatic tires, in general, anisoprene rubber such as natural rubber is used as the rubber componentand a combination of carbon black and silica is used as the reinforcingfiller so that an excellent balance between abrasion resistance and thelow heat generating property is achieved.

[0007] A rubber composition comprising an isoprene rubber as the rubbercomponent, however, has a problem in that the modulus tends to decreasedue to reversion under over-cure and the low heat generating propertytends to deteriorate. In particular, in tires of large sizes such astires having a total gauge at the hump position in the tread portion of50 mm or greater, problems arise in that the low heat generatingproperty deteriorates and abrasion resistance decreases.

[0008] It is frequently conducted that a loss lowering agent (an agentfor providing the property of less heat generation) such as5-nitroso-8-hydroxyquinoline as a typical example is added to the abovecomposition in order that the low heat generating property of a heavyduty tire is improved. The effect of conventional loss lowering agentssuch as that described above, however, varies depending on the degree ofvulcanization and a problem arises in that the effect of improving thelow heat generating property is not sufficiently exhibited for tires ,in particular, of large sizes since the modulus decreases due toover-cure which tends to take place in production of such tires.

SUMMARY OF THE INVENTION

[0009] The present invention has an object of providing a rubbercomposition which exhibits improved abrasion resistance, heat resistanceand low heat generating property and is advantageously used for treadrubber of heavy duty pneumatic tires, and it is another object toprovide a heavy duty pneumatic tire using the rubber composition fortread rubber.

[0010] As a result of intensive studies by the present inventor, it wasfound that the objects can be achieved by a rubber composition whichcomprises a rubber component comprising a modified styrene-butadienecopolymer rubber having a tin atom introduced into the molecular chain,which is obtained by a solution polymerization and natural rubber or ansynthetic isoprene rubber as the essential components at a specificcompounding ratio and a hydrazide compound.

[0011] The present invention has been completed based on this knowledge.

[0012] The present invention provides a rubber composition whichcomprises (A) a rubber component comprising 15 to 55% by weight of (i) amodified styrene-butadiene copolymer rubber having a tin atom introducedinto the molecular chain, which is obtained by a solutionpolymerization, 45 to 85% by weight of (ii) at least one rubber selectedfrom natural rubber and synthetic isoprene rubbers and (B) a hydrazidecompound.

[0013] The present invention also provides a heavy duty pneumatic tirewhich comprises a tread rubber comprising a rubber composition describedabove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The rubber composition of the present invention comprises (A) arubber component comprising (i) a modified styrene-butadiene copolymerrubber, (ii) at least one rubber selected from natural rubber andsynthetic isoprene rubbers and, where desired, (iii) other conjugateddiene rubbers.

[0015] The above modified styrene-butadiene copolymer rubber ofcomponent (i) is obtained by a solution polymerization and modified byintroducing tin atom into the molecular chain.

[0016] The modified styrene-butadiene copolymer rubber can be produced,for example, in accordance with the following processes.

[0017] In the first two processes, 1,3-butadiene and styrene are used asthe raw materials. The raw materials are anionically copolymerized in asolution by using an alkali metal compound, preferably a lithiumcompound, as a polymerization initiator and a styrene-butadiene basecopolymer having a reactive chain ends is obtained. The desired modifiedstyrene-butadiene copolymer rubber can be obtained by modifying theobtained copolymer with a tin compound.

[0018] In the third process, 1,3-butadiene and styrene are used as theraw materials. The raw materials are anionically copolymerized in asolution by using an alkali metal compound, preferably a lithiumcompound, having a tin compound as a polymerization initiator, and astyrene-butadiene base copolymer having a reactive chain end isobtained. The reactive chain end may be modified with a modifier, suchas a tin compound, an alkoxysilane compound, a nd a nitrogen-containingcompound, or may be terminated without modification.

[0019] In the forth process, 1,3-butadiene and styrene are used as theraw materials. The raw materials are anionically copolymerized in asolution by using an alkali metal compound, preferably a lithiumcompound, having a tin atom and a nitrogen atom as a polymerizationinitiator, and a styrene-butadiene copolymer having a tin atom and anitrogen atom in its molecule is obtained.

[0020] In the fifth process, 1,3-butadiene and styrene and a compoundhaving a tin atom are used as the raw materials. The raw materials areanionically copolymerized in a solution by using an alkali metalcompound, preferably a lithium compound, as a polymerization initiator,and a styrene-butadiene base copolymer having a reactive chain end isobtained. The reactive chain end may be modified with a modifier, suchas a tin compound, an alkoxysilane compound, and a nitrogen-containingcompound, or may be terminated without modification.

[0021] These processes may be used in combination.

[0022] By using any of third through fifth processes, a copolymer havinga tin atom in its molecule can be obtained without a modification step.

[0023] As the lithium compound used as the polymerization initiator inthe first, second and fifth processes, a hydrocarbyllithium compoud or alithium amide compound is preferably used. When a hydrocarbyllithiumcompound is used, a styrene-butadiene base copopolymer in whichinitiating chain end has a hydrocarbyl group can be obtained. When alithium amide compound is used as the polymerization initiator, astyrene-butadiene base copolymer in which the initiating chain end has agroup having a nitrogen atom can be obtained.

[0024] A base copolymer used here means a copolymer before a terminationstep, which has a reactive end.

[0025] As the hydrocarbyllithium compound, those having a hydrocarbylgroup having 2 to 20 carbon atoms are preferable. Examples of thehydrocarbyllithium compound include ethyllithium, n-propyllithium,isopropyllithium, n-butyllithium, sec-butyllithium, tert-octyllithium,n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyllithium,4-phenylbutyllithium, cyclohexyllithium, cyclopentyllithium and reactionproducts of diispropenylbenzene and butyllithium. Among these compounds,n-butyllithium is more preferable.

[0026] Examples of the lithium amide compound include lithiumhexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithiumheptamethyleneimide, lithium dodecamethyleneimide, lithiumdimethylamide, lithium diethylamide, lithium dibutylamide, lithiumdipropylamide, lithium diheptylamide, lithium dihexylamide, lithiumdioctylamide, lithium bis(2-ethylhexylamide), lithium didecylamide,lithium N-methylpiperadide, lithium ethylpropylamide, lithiumethylbutylamide, lithium methylbutylamide, lithium ethylbenzylamide andlithium methylphenetylamide. Among these compounds, cyclic lithiumamides such as lithium hexamethyleneimide, lithium pyrrolidide, lithiumpiperidide, lithium heptamethyleneimide and lithium dodecamethyleneimideare more preferable and lithium hexamethyleneimide and lithiumpyrrolidide are particularly preferable.

[0027] As the lithium compound used as a polymerization initiator in thethird process, a triorganotin lithium compound such as tributyltinlithium and trioctyltin lithium may be used.

[0028] As lithium compound having a tin atom and a nitrogen atom used inthe forth process, a triorganoamide stannyllithium represented by thegeneral formula (a) shown bellow or a triorganoimide stannyllithiumrepresented by the general formula (b) shown bellow may preferably beused.

[0029] wherein R¹ and R² each independently represents an aliphatichydrocarbon group containing 1 to 20 carbon atoms, an aromatichydrocarbon group containing 5 to 20 carbon atoms, or a cycloaliphatichydrocarbon group containing 3 to 20 carbon atoms; and triorganotinlithium compound represented by general formula (b):

[0030] wherein X represents: a saturated cyclic group having the formula(CR³R⁴)n; a saturated cyclic group having the formula (CR⁵R⁶)_(m)—Y—(CR⁵R⁶), wherein Y represents NR⁷ or O; or imine compounds having acarbon-carbon double bond; wherein R³, R⁴, R⁵ and R⁶ each independentlyrepresents hydrogen or an aliphatic hydrocarbon group containing 1 to 10carbon atoms, an aromatic hydrocarbon group containing 5 to 10 carbonatoms, or a cycloaliphatic hydrocarbon group containing 3 to 10 carbonatoms, R⁷ is an aliphatic hydrocarbon group containing 1 to 10 carbonatoms, an aromatic hydrocarbon group containing 5 to 10 carbon atoms, ora cycloaliphatic hydrocarbon group containing 3 to 10 carbon atoms, nrepresents an integer between 3 and 10, and the sum of m and is between2 and 9.

[0031] Examples of the preferable triorganotin lithium compound amongthem include, tripyrrolididestannyllithium,trihexamethyleneimidestannyllithium, tri(diethyl)amidestannyllithium andtri(dipropyl)amidestannyllithium.

[0032] An objective styrene-butadiene copolymer can also be obtained byintroducing a third monomer containing a tin atom.

[0033] As the third monomer copolymerized with styrene and1,3-butadiene, a compound represented by the following general formula(c) or (d) may preferably be used.

[0034] wherein R⁸, R⁹ and R¹⁰ each represents an aliphatic hydrocarbongroup having 1 to 30 carbon atoms, an alicyclic hydrocarbon group or anaromatic hydrocarbon group and the groups represented by R⁸, R⁹ and R¹⁰may be the same with or different from each other;

[0035] Formula (d):

[0036] wherein R¹¹R¹²C═CR¹³—, R¹⁴, R¹⁵, R¹⁶ and R¹⁷ each represent agroup bonded to the benzene group, R¹¹, R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷,R¹⁸, R¹⁹, R²⁰, R²¹ and R²² each represent hydrogen atom, an aliphatichydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbongroup or an aromatic hydrocarbon group, R²⁰, R²¹ and R²² each representan aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclichydrocarbon group or an aromatic hydrocarbon group and the atom or thegroups represented by R¹¹ to R²² may be the same with or different fromeach other.

[0037] Preferable examples of the compound represented by generalformula (c) include 2-tributylstannyl-1,3-butadiene,2-trioctylstannyl-1,3-butadiene, 2-tricyclohexyl-1,3-butadiene,2-triphenylstannyl-1,3-butadiene, 2-dibutylphenylstannyl-1,3-butadieneand 2-diphenyloctylstannyl-1,3-butadiene. Preferable examples of thecompound represented by general formula (d) include m-vinylbenzyl-tributyltin, m-vinylbenzyltrioctyltin, m-vinylbenzyltriphenyltin,m-(1-phenylvinyl)benzyltributyltin, p-isomers of these compounds andmixtures of the m-isomers and the p-isomers of these compounds.

[0038] A triorganoamide stannyllithium or a triorganoamidestannyllithium is preferably used.

[0039] The triorganotin lithiums are described in U.S. Pat.No.5,502,129, which is hereby incorporated by reference, and thetriorganoamide stannyllithiums and triorganoimide stannyllithiums aredescribed in U.S. Pat No.5,463,003, which is hereby incorporated byreference,

[0040] The process for producing the styrene-butadiene copolymer usingthe above lithium compound as the initiator by the anionicpolymerization is not particularly limited and a conventional processcan be used.

[0041] Specifically, an objective styrene-butadiene copolymer can beobtained by an anionic polymerization of styrene and 1,3-butadiene in anorganic solvent which is inert to the reaction, for example, in ahydrocarbon solvent such as an aliphatic, alicyclic or aromatichydrocarbon compound, using the above lithium compound as apolymerization initiator and, where desired, in the presence of arandomizer.

[0042] The temperature in the polymerization reaction is selected, ingeneral, in the range of −80 to 150° C. and preferably in the range of−20 to 100° C. The polymerization reaction may be conducted under apressure generated by the reaction system. In general, however, it ispreferable that the operations in the reaction are conducted under asufficient pressure which can keep the monomers substantially in theliquid phase. Where desired, a higher pressure may be applied and such apressure can be obtained in accordance with a suitable method, forexample, by charging the reactor with a gas inert to the polymerizationreaction.

[0043] In the styrene-butadiene base copolymer obtained above, theinitiating chain end has a hydrocarbyl group or a group having anitrogen atom while the other chain end is polymerization active. Thedesired modified styrene-butadiene copolymer rubber can be obtained byreacting a tin compound with the polymerization active chain end of theabove copolymer.

[0044] Examples of the tin compound include tin tetrachloride,tributyltin chloride, dioctyltin dichloride, dibutyltin dichloride andtriphenyltin chloride.

[0045] In component (A) of the rubber composition of the presentinvention, at least one rubber selected from natural rubber andsynthetic isoprene rubber is used as component (ii). The syntheticisoprene rubber is obtained by polymerizing isoprene monomer. Inparticular, synthetic isoprene rubber having about 98% of thecis-1,4structure has basic properties close to those of natural rubbersince its molecular structure is very close to that of natural rubber.

[0046] Examples of the other conjugated diene rubbers of component (ii)which are used, where desired, include polybutadiene rubbers (BR), otherstyrene-butadiene rubbers (SBR), acrylonitrile-butadiene rubbers (NBR),chloroprene rubbers (CR) and butyl rubbers (IIR). The other conjugatedrubber may be used singly or in combination of two or more.

[0047] In the rubber composition of the present invention, thecompounding ratio of the components in component (A) are as follows: 15to 55% by weight of component (i); 45 to 85% by weight of component(ii); and 0 to 40% by weight of component (iii). When the compoundingratio of the components are outside the above ranges, a rubbercomposition having the desired physical properties cannot be obtained.It is preferable that component (A) comprises 15 to 55% by weight ofcomponent (i) and 85 to 45% by weight of component (ii) from thestandpoint of the balance among the physical properties.

[0048] Examples of the hydrazide compound used as component (B) in therubber composition of the present invention include compoundsrepresented by general formula (I):

[0049] In the above general formula (I), A represents an arylene group,a divalent hydantoin residue or a saturated or unsaturated divalentaliphatic hydrocarbon group having 1 to 18 carbon atoms. The arylenegroup include divalent aromatic heterocyclic groups. As the arylenegroup, phenylene group and naphthylene group are preferable and thesegroups may have suitable substituents such as lower alkyl groups andlower alkoxyl groups on the ring. The divalent hydantoin residue mayhave suitable substituents such as lower alkyl groups and lower alkoxylgroups on the ring. Examples of the saturated or unsaturated divalentaliphatic hydrocarbon group having 1 to 18 carbon atoms include alkylenegroups having 1 to 18 carbon atoms and alkenylene groups having 2 to 18carbon atoms. These groups may be linear groups or branched groups.Examples of the alkylene group and the alkenylene group includemethylene group, ethylene group, propylene group, butylene group,hexylene group, octylene group, decylene group, vinylene group, allylenegroup, propenylene group, butenylene group, hexenylene group, octenylenegroup and decenylene group,

[0050] Z represents a hydrogen atom, a hydroxyl group, an amino group ora group represented by the following formula:

[0051] R²³ to R²⁶ each represent a hydrogen atom, or a hydrocarbyl grouphaving 1 to 18 carbon atoms. The R²³ to R²⁶ may be the same with ordifferent from each other. The groups represented by R²³ and R²⁴ may bebonded to each other and form a ring structure and the groupsrepresented by R²⁵ and R²⁶ may be bonded to each other and form a ringstructure. Examples of the hydrocarbyl group having 1 to 18 carbon atomsinclude linear and branched alkyl groups having 1 to 18 carbon atoms,linear and branched alkenyl groups having 2 to 18 carbon atoms,cycloalkyl groups having 3 to 18 carbon atoms, aryl groups having 3 to18 carbon atoms and aralkyl groups having 7 to 18 carbon atoms. Theabove cycloalkyl groups, aryl groups and aralkyl groups may havesuitable substituents such as lower alkyl groups, low alkoxyl groups,amino group, amino groups substituted with alkyl groups and hydroxylgroup on the ring.

[0052] Examples of the alkyl group described above include methyl group,ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutylgroup, sec-butyl group, tert-butyl group, pentyl group, hexyl group,octyl group and decyl group. Examples of the alkenyl group include vinylgroup, allyl group, propenyl group, butenyl group, hexenyl group,octenyl group and decenyl group. Examples of the cycloalkyl groupinclude cyclopentyl group, cyclohexyl group and methylcyclohexyl group.Examples of the aryl group include phenyl group, tolyl group, xylylgroup, naphthyl group and methylnaphthyl group. Examples of the aralkylgroup include benzyl group, phenetyl group and naphthylmethyl group.

[0053] Among the compounds represented by general formula (I), compoundsrepresented by general formula in which A represents an arylene groupand Z represents hydroxyl group are preferable. Hydrazide compoundsrepresented by general formula (I-a):

[0054] and hydrazide compounds represented by general formula (I-b):

[0055] are more preferable from the standpoint of the properties of theresulting rubber composition. In the above general formulae, R²³ and R²⁴are as defined above.

[0056] Examples of the hydrazide compound represented by the abovegeneral formula

[0057] (I) include 1-hydroxy-N′(1-methylethylidene)-2-naphthoic acidhydrazide,

[0058] 1-hydroxy-N′-(1-methylpropylidene)-2-naphthoic acid hydrazide,

[0059] 1-hydroxy-N′-(1-methylbutylidene)-2-naphthoic acid hydrazide,

[0060] 1-hydroxy-N′-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide,

[0061] 1-hydroxy-N′-(2,6-dimethyl-4-heptylidene)-2-naphthoic acidhydrazide,

[0062] 2-hydroxy-N′-(1-methylethylidene)-3-naphthoic acid hydrazide,

[0063] 2-hydroxy-N′-(1-methylpropylidene)3-naphthoic acid hydrazide,

[0064] 2-hydroxy-N′-(1-methylbutylidene)-3-naphthoic acid hydrazide,

[0065] 2-hydroxy-N′-(1,3-dimethylbutylidene)-3-naphthoic acid hydrazide,

[0066] 2-hydroxy-N′-(2,6-dimethyl-4-heptylidene)3-naphthoic acidhydrazide, isophthalic

[0067] acid di(1-methylethylidene)hydrazide, isophthalic acid

[0068] di(1-methylpropylidene)-hydrazide, isophthalic acid

[0069] di(1-methylbutylidene)-hydrazide, isophthalic aciddi(1,3-dimethylbutylidene)hydrazide,

[0070] isophthalic acid di(2,6-dimethyl-4-heptylidene)hydrazide,isonicotinic acid

[0071] (1-methylethylidene)-hydrazide, isonicotinic acid(1-methylpropylidene)hydrazide,

[0072] isonicotinic acid (1-methylbutylidene)hydrazide, isonicotinicacid

[0073] (2,6-dimethyl-4-heptylidene)hydrazide, isonicotinic acid

[0074] (1,3-dimethylbutylidene)-hydrazide,N′-(1-methylethylidene)salicylic acid hydrazide,

[0075] N′-(1-methylpropylidene)salicylic acid hydrazide,N′-(1-methylbutylidene)-salicylic

[0076] acid hydrazide, N′-(1,3-dimethylbutylidene)salicylic acidhydrazide,

[0077] N′-(2,6-dimethyl-4-heptylidene)salicylic acid hydrazide,

[0078] N′-(1-methylethylidene)benzoic acid hydrazide,N′-(1-methylpropylidene)benzoic acid

[0079] hydrazide, N′-(1,3-dimethylbutylidene)benzoic acid hydrazide,

[0080] N′-(benzylidene)benzoic acid hydrazide,

[0081] N′-(4-dimethylaminophenyl-methylene)benzoic acid hydrazide,

[0082] N′-(4-methoxyphenylmethylene)benzoic acid hydrazide,

[0083] N′-(4-hydroxyphenylmethylene)benzoic acid hydrazide,

[0084] N′-(1-phenylethylidene)benzoic acid hydrazide,N′-(diphenylmethylene)-benzoic acid

[0085] hydrazide, N′-(1-(2,4-dihydroxyphenyl)benzylidene)benzoic acidhydrazide,

[0086] N′-(1-methylethylidene)-1-naphthoic acid hydrazide,

[0087] N′-(1-methylpropylidene)1-naphthoic acid hydrazide,

[0088] N′-(1,3-dimethyl-butylidene)-1-naphthoic acid hydrazide,

[0089] N′-(benzylidene)-1-naphthoic acid hydrazide,

[0090] N′-(4-dimethylaminophenylmethylene)-1-naphthoic acid hydrazide,

[0091] N′-(4-methoxyphenylmethylene)-1-naphthoic acid hydrazide,

[0092] N′-(4-hydroxyphenylmethylene)-1-naphthoic acid hydrazide,

[0093] N′-(1-phenylethylidene)-1-naphthoic acid hydrazide,

[0094] N′-(diphenylmethylene)-1-naphthoic acid hydrazide,

[0095] N′-(1-(2,4-dihydroxyphenyl)benzylidene)-1-naphthoic acidhydrazide,

[0096] N′-(1-methylethylidene)-2-naphthoic acid hydrazide,

[0097] N′-(1-methylpropylidene)-2-naphthoic acid hydrazide,

[0098] N′-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide,

[0099] N′-(benzylidene)-2- naphthoic acid hydrazide,

[0100] N′-(4-dimethylaminophenylmethylene)-2-naphthoic acid hydrazide,

[0101] N′-(4-methoxyphenylmethylene)-2-naphthoic acid hydrazide,

[0102] N′-(4-hydroxyphenylmethylene)2-naphthoic acid hydrazide,

[0103] N′-(1-phenylethylidene)-2-naphthoic acid hydrazide,

[0104] N′-(diphenylmethylene)-2-naphthoic acid hydrazide,

[0105] N′-(1-(2,4-dihydroxy-phenyl)benzylidene)-2-naphthoic acidhydrazide,

[0106] N′-(4-methylethylidene)-propionic acid hydrazide,N′-(1-methylpropylidene)propionic

[0107] acid hydrazide, N′-(1,3-dimethylbutylidene)propionic acidhydrazide,

[0108] N′-(1-benzylidene)propionic acid hydrazide,

[0109] N′-(4-dimethylaminophenyl-methylene)propionic acid hydrazide,

[0110] N′-(4-methoxyphenylmethylene)-propionic acid hydrazide,

[0111] N′-(4-hydroxyphenylmethylene)propionic acid hydrazide,

[0112] N′-(1-phenylethylidene)propionic acid hydrazide,N′-(diphenylmethylene)propionic

[0113] acid hydrazide, N′-(1-(2,4-dihydroxy-phenyl)benzylidene)propionicacid hydrazide,

[0114] N′-(4-methylethylidene)-2-methylpropionic acid hydrazide,

[0115] N′-(1-methylpropylidene)-2-methyl-propionic acid hydrazide,

[0116] N′-(1,3-dimethylbutylidene)2-methylpropionic acid hydrazide,

[0117] N′-(benzylidene)2-methylpropionic acid hydrazide,

[0118] N′-(4-dimethylaminophenylmethylene)-2-methylpropionic acidhydrazide,

[0119] N′-(4-methoxyphenylmethylene)-2-methylpropionic acid hydrazide,

[0120] N′-(4-hydroxyphenylmethylene)-2-methylpropionic acid hydrazide,

[0121] N′-(1-phenylethylidene)-2-methylpropionic acid hydrazide,

[0122] N′-(diphenylmethylene)-2-methylpropionic acid hydrazide,

[0123] N′-(1-(2,4-dihydroxy-phenyl)benzylidene)-2-methylpropionic acidhydrazide,

[0124] N′-(1-methylethylidene)-2,2-dimethylpropionic acid hydrazide,

[0125] N′-(1-methylpropylidene)-2,2-dimethylpropionic acid hydrazide,

[0126] N′-(1,3-dimethylbutylidene)-2,2-&methylpropionic acid hydrazide,

[0127] N′-(benzylidene)-2,2-dimethylpropionic acid hydrazide,

[0128] N′-(4-dimethylamino-phenylmethylene)-2,2-dimethylpropionic acidhydrazide,

[0129] N′-(4-methoxyphenylmethylene)-2,2-dimethylpropionic acidhydrazide,

[0130] N′-(4-hydroxyphenylmethylene)-2,2-dimethylpropionic acidhydrazide,

[0131] N′-(1-phenylethylidene)-2,2-dimethylpropionic acid hydrazide,

[0132] N′-(diphenylmethylene)-2,2-dimethylpropionic acid hydrazide and

[0133] N′-(1-(2,4-dihydroxyphenyl)benzylidene)-2,2-dimethylpropionicacid hydrazide.

[0134] Examples of the preferable hydrazide compounds among the abovehydrazide compounds include1-hydroxy-N′-(1-methylethylidene)-2-naphthoic acid hydrazide,

[0135] 1-hydroxy-N′-(1-methylpropylidene)2-naphthoic acid hydrazide,

[0136] 1-hydroxy-N′-(1-methylbutylidene)-2-naphthoic acid hydrazide,

[0137] 1-hydroxy-N′-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide,

[0138] 1-hydroxy-N′-(2,6-dimethyl-4-heptylidene)-2-naphthoic acidhydrazide,

[0139] 2-hydroxy-N′-(1-methylethylidene)-3-naphthoic acid hydrazide,

[0140] 2-hydroxy-N′-(1-methylpropylidene)-3-naphthoic acid hydrazide,

[0141] 2-hydroxy-N′-(1-methylbutylidene)3-naphthoic acid hydrazide,

[0142] 2-hydroxy-N′-(1,3-dimethylbutylidene)-3-naphthoic acid hydrazide,

[0143] 2-hydroxy-N′-(2,6-dimethyl-4-heptylidene)-3-naphthoic acidhydrazide, isophthalic

[0144] acid di(1-methylethylidene)hydrazide, isophthalic acid

[0145] di(1-methylpropylidene)hydrazide, isophthalic aciddi(1-methylbutylidene)hydrazide,

[0146] isophthalic acid di(1,3-dimethylbutylidene)hydrazide, isophthalicacid

[0147] di(2,6diethyl-4heptylidene)hydrazide, isonicotinic acid

[0148] (1-methylethylidene)hydrazide, isonicotinic acid(1-methylpropylidene)hydrazide,

[0149] isonicotinic acid (1-methylbutylidene)hydrazide, isonicotinicacid

[0150] (1,3-dimethylbutylidene)hydrazide, isonicotinic acid

[0151] (2,6-dimethyl-4-heptylidene)hydrazide,N′-(1-methylethylidene)salicylic acid

[0152] hydrazide, N′-(1-methylpropylidene)salicylic acid hydrazide,

[0153] N′-(1-methylbutylidene)salicylic acid hydrazide,N′-1,3-dimethylbutylidene)salicylic

[0154] acid hydrazide and N′-(2,6-dimethyl-4-heptylidene)salicylic acidhydrazide.

[0155] Compounds represented by general formula (I-a) and compoundsrepresented by general formula (I-b) are more preferable. Examples ofthe more preferable compounds include2(hydroxy-N′-(1-methylethylidene)-3-naphthoic acid hydrazide,

[0156] 2-(hydroxy-N′-(1-methylpropylidene)-3-naphthoic acid hydrazide,

[0157] 2-hydroxy-N′-(1-methylbutylidene)3-naphthoic acid hydrazide,

[0158] 2-hydroxy-N′-(1,3-dimethylbutylidene)-3-naphthoic acid hydrazide,

[0159] 2-(hydroxy-N′-(2,6-dimethyl-4-heptylidene)-3-naphthoic acidhydrazide,

[0160] N′-(1-methylethylidene)salicylic acid hydrazide,N′-(1-methylpropylidene)-salicylic

[0161] acid hydrazide, N′-1-methylbutylidene)salicylic add hydrazide,

[0162] N′-(1,3-dimethylbutylidene)salicylic acid hydrazide and

[0163] N′-(2,6-dimethyl-4-heptylidene)salicylic acid hydrazide.

[0164] The hydrazide compound of component (B) suppresses the decreasein modulus due to reversion under over-cure and the deterioration in thelow heat generating property and abrasion resistance.

[0165] In the present invention, the hydrazide compound of component (B)may be used singly or in combination of two or more. The amount ofcomponent (B) used in the composition is selected, preferably, in therange of 0.05 to 5 parts by weight per 100 parts by weight of the rubbercomponent (A). When the amount is smaller than 0.05 parts by weight,there is a possibility that the decrease in modulus is not sufficientlysuppressed. When the amount exceeds 5 parts by weight, the effect is notenhanced to the degree expected from the amount and economicdisadvantage occasionally arises. From the standpoint of the effect andeconomy, it is more preferable that the amount of component (B) is inthe range of 0.3 to 3 parts by weight

[0166] The rubber composition of the present invention may furthercomprise carbon black as component (C). As the carbon black, thosehaving a specific surface area by nitrogen adsorption (N₂SA) of 50 m²/gor greater is preferable. When N₂SA is smaller than 50 m²/g, asufficient abrasion resistance may not be obtained. As the value of N₂SAbecomes greater, the low heat generating property tends to bedeteriorated From the standpoint of the desirable balance betweenabrasion resistance and the low heat generating property, it is morepreferable that N₂SA is in the range of 80 to 160 m²/g. N₂SA is obtainedin accordance with the method of ASTM D3037-88.

[0167] The above carbon black is not particularly limited and a desiredcarbon black can suitably be selected from carbon blacks which areconventionally used as the reinforcing filler for rubber. Examples ofthe preferable carbon black include FEF, SRF, HAF, ISAF and SAF. Amongthese carbon blacks, HAF, ISAF and SAF are more preferable due toexcellent abrasion resistance.

[0168] In the present invention, the carbon black of component (C) maypreferably be used, in an amount in the range of 20 to 70 parts byweight per 100 parts by weight of the rubber component of component (A).When the amount is smaller than 20 parts by weight, there is apossibility that sufficient abrasion resistance is not exhibited. Whenthe amount exceeds 70 parts by weight, problems such as deterioration inthe low heat generating property, poor dispersion and a decrease inabrasion resistance may arise. From the standpoint of abrasionresistance, the heat generating property and dispersion, it is morepreferable that the amount of carbon black is in the range of 30 to 60parts by weight.

[0169] The rubber composition of the present invention firer comprisessilica as component (D), where desired. As the silica, those having aspecific surface area by nitrogen adsorption (N₂SA ) in the range of 160to 260 m²/g or greater and a dibutyl phthalate absorption (DBP) in therange of 180 to 260 ml/100 g is preferable. When N₂SA is smaller than160 m²/g or DBP is smaller than 180 ml/100 g, there is a possibilitythat abrasion resistance is insufficient. When N₂SA exceeds 260 m²/g orDBP exceeds 260 ml/100 g, dispersion becomes poor and problems such asdeterioration in the low heat generating property and a decrease inabrasion resistance may arise.

[0170] N₂SA described above is a value measured in accordance with themethod of ASTM D4820-93 after drying a sample at 300° C. for 1 hour. DBPdescribed above is a value measured in accordance with the method ofASTM D2414-93.

[0171] Examples of the silica include wet silica (silica hydrate), drysilica (silicic acid anhydride), calcium silicate and aluminum silicate.Among these substances, wet silica is preferable.

[0172] In the present invention, the silica of component (D) ispreferably used in an amount of 30 parts by weight or smaller per 100parts by weight of the rubber component (A). When the amount exceeds 30parts by weight, there is a possibility that the low heat generatingproperty deteriorates. It is more preferable that the amount of silicais 20 parts by weight or smaller.

[0173] The rubber composition of the present invention comprises therubber component (A), the hydrazide compound (B) and, where desired, thecarbon black (C) and/or the silica (D), as described above. The rubbercomposition may further comprise vulcanizing agents, vulcanizationaccelerators, auxiliary vulcanization accelerators, antioxidants,softeners and other compounding ingredients which are conventionallyused.

[0174] The heavy duty pneumatic tire of the present invention can beproduced by using the above rubber composition for tread rubber, formedand vulcanized under a conventional condition of vulcanization.

[0175] The gas to be charged inside the tire may be air and/or an inertgas such as nitrogen.

[0176] To summarize the advantages of the present invention, the rubbercomposition of the present invention exhibits an excellent balance amongthe low heat generating property, heat resistance and abrasionresistance and can be advantageously applied to a tread rubber of aheavy duty pneumatic tire.

EXAMPLES

[0177] The present invention will be described more specifically withreference to examples in the following. However, the present inventionis not limited to the examples.

Examples 1 to 3 and Comparative Examples 1 to 5

[0178] One hundred parts by weight of rubber components having theCompositions shown in Table 1,2-hydroxy-N′-(1,3-dimethylbutylidene)-3-naphthoic acid hydrazide (BMH)in amounts shown in Table 1, 50 parts by weight of carbon black of theSAF grade, 1.0 part by weight of wax “WMO2” (manufactured by SEIKOKAGAKU Co., Ltd.), 2.0 parts by weight of stearic acid, 1.3 parts byweight of an antioxidant 6C(N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine), 3.5 parts byweight of zinc oxide, 1.0 part by weight of a vulcanization acceleratorCZ(N-cyclohexyl-2-benzothiazyl sulfeneamide) and 1.2 parts by weight ofsulfur were compounded and rubber compositions were prepared. andvulcanized at 145° C. for 30 minutes. The prepared rubber compositionswere used for tread rubbers and tires having sized (11R22.5) wereprepared

[0179] Samples were taken from the vulcanized rubbers and the low heatgenerating property and the heat resistance were obtained in accordancewith the method described in the following. The abrasion resistance wasevaluated using tires having the above tread rubbers in accordance withthe method described in the following.

[0180] (1) Low heat generating property

[0181] Using a test piece having a width of 5 mm, E′ (tan δ) wasmeasured under the condition of a stain of ±2%, a frequency of 52 Hz anda temperature of 100° C. by a viscoelasticity spectrometer manufacturedby TOYO SEIKI SEISAKUSHO Co., Ltd. The reverse of the value of tan δ wasused as the Low heat generating property. The result is expressed as anindex based on the result of Comparative Example 1 which is set at 100.The greater the value, the better the low heat generating property.

[0182] (2) Heat resistance

[0183] From a tread of a tire after the abrasion test, a block of10×10×200 mm was obtained as a sample. A cut of 30 mm was formed in thesample at the center in the direction of the thickness. Portions of thesample at both sides of the formed cut were pulled apart and the teastrength was measured. The result is expressed as an index based on theresult of Comparative Example 1 which is set at 100. The greater thevalue, the better the heat generating property.

[0184] (3) Abrasion resistance

[0185] Tires of a size of 11R22.5 having a conventional structure wereprepared. For the tread portion, rubber compositions shown in Table 1(Examples and Comparative Example) were used. The tires were inflated toan inner pressure described below and attached to rims described below.The assembled wheels were each attached to an automobile at the sameposition. The automobile was driven for the distance of 20,000 km on arough road and then the amount of abrasion was measured.

[0186] The inner pressure is the air pressure corresponding to themaximum load (the maximum ability of bearing the load) of a single wheelof the appropriate size described as the standard in “JATMA Year Book”edited by the Japanese Automobile Tire Manufacturers Association. Therim is the standard rim having the appropriate size described in theabove standard.

[0187] The reverse of the amount of abrasion was used as the abrasionresistance. The result is expressed as an index based on the result ofComparative Example 1 which is set at 100. The greater the value, thebetter the heat generating property. TABLE 1-1 Comparative Example 1Example 2 Example 3 Example 1 Rubber component (part by weight) naturalrubber 80 60 50 100 E-SBR¹⁾ — — — — S-SBR²⁾ 20 40 20 — BR³⁾ — — 30 —BMH⁴⁾(part by weight) 1.0 1.0 1.0 — Low heat generating 112 125 126 100Property (index) Heat Resistance 122 117 115 100 (index) Abrasionresistance 114 116 125 100 (index)

[0188] TABLE 1-2 Comparative Comparative Comparative Comparative Example2 Example 3 Example 4 Example 5 Rubber component (part by weight)natural rubber 80 80 60 60 E-SBR¹⁾ 20 — 40 — S-SBR²⁾ — 20 — 40 BR³⁾ — —— — BMH⁴⁾ — — — — (part by weight) Low heat 94 100 87 110 generatingProperty (index) Heat 105 106 112 101 Resistance (index) Abrasion 107107 110 110 resistance (index) # JSR #1500. # the trade name: FSCHEMICAL HX765.

[0189] As shown in Table 1, the rubber compositions of the presentinvention comprising the styrene-butadiene rubber obtained by a solutionpolymerization having a Sn atom in its molecule, and a hydrazidecompound exhibit an excellent balance between physical properties of thelow heat generating property, heat resistance and abrasion resistance.

What is claimed is:
 1. A rubber composition obtained by compounding (A)a rubber component comprising 15 to 55% by weight of (i) a modifiedstyrene-butadiene copolymer rubber which is obtained by a solutionpolymerization and has a tin atom introduced into its molecular chain,45 to 85% by weight of (ii) at least one rubber selected from naturalrubber and synthetic isoprene rubbers, and (B) a hydrazide compound. 2.A rubber composition according to claim 1, wherein component (A)comprises 15 to 55% by weight of component (i) and 85 to 45% by weightof component (ii).
 3. A rubber composition according to claim 1, whereinthe modified styrene-butadiene copolymer rubber of component (i) ofcomponent (A) is obtained by modifying a styrene-butadiene copolymerwhich is obtained by a solution polymerization using a lithium compoundas an initiator with a tin compound.
 4. A rubber composition accordingto claim 1, wherein the hydrazide compound of component (B) is at leastone compound selected from naphthoic acid hydrazides and salicylic acidhydrazides.
 5. A rubber composition according to claim 1, wherein 0.05to 5 parts by weight of component (B) per 100 parts by weight ofcomponent (A) is compounded.
 6. A rubber composition according to ofclaim 1, wherein 20 to 70 parts by weight of (C) carbon black per 100parts by weight of component (A) is further compounded.
 7. A heavy dutypneumatic tire having a tread wherein the rubber compositionconstituting the tread is a rubber composition described in claim 1.